Coating composition

ABSTRACT

A protective coating composition in an organic liquid carrier comprising a polymeric film forming binder, the polymeric binder comprising by weight: 
     (a) 50% to 100% of an epoxy-polyester block copolymer being the reaction product of a preformed epoxy resin and a preformed carboxyl functional, and (b) 0 to 50% of a crosslinker where the sum of (a) and (b) is 100%, 
     characterized in that the carboxyl functional polyester prepolymer is the reaction product of one or more polyols with one or more dicarboxylic acids or their anhydrides, where the dicarboxylic acids or anhydrides comprise a mixture of (i) 20% to 45% of an aromatic dicarboxylic acid or its anhydride, (ii) 55% to 80% of cyclohexane dicarboxylic acid, and (iii) 0 to 10% other aliphatic dicarboxylic acid, where the sum of (i), (ii), and (iii) is 100% based on the weight of the dicarboxylic acid and anhydride components.

This invention relates to a coating composition, its preparation anduse. Metal food and drink containers, often referred to as cans, areusually coated on the inside to prevent reaction between the contentsand the metal from which the can is formed. Such reaction leads both tounwanted deterioration of the can and also potentially damaging effectson the contents, particularly in terms of changes in quality and taste.Without an interior coating, most cans of food or drink would not remainusable for very long. The coating is often applied to the flat metal byroller coating before the can is formed and then dried or cured in astoving operation. The can is then formed from the flat metal by adrawing process before being filled with food or drink and finallysealed up.

The coatings are required to have very good flexibility, adhesion,sterilisation resistance and stability properties. Flexibility andadhesion are essential if the coating is to remain intact during the canformation process when the coated flat metal sheet is drawn into theform of the can. When the cans are filled with food, the contents areusually sterilised by heating the sealed can to temperatures of around130° C. for 1 to 2 hours (depending on the nature of the food). Thecoating is then in direct contact with the contents of the can for aconsiderable period of time which could be many years. Duringsterilisation and subsequent storage, the coating is required tomaintain its integrity so as to prevent corrosion of the metal can andto prevent metal migration into the can contents. Additionally, thecoating must not impair the contents by releasing unwanted material orby altering the flavour or appearance. These resistance propertiesimpact not only on the shelf life of the product but also on publichealth and safety. Thus, there are particularly stringent and specificrequirements of coating compositions for can interiors which aredifferent from those for other coatings.

One known type of coating composition for cans is based on an epoxyresin. Epoxy resin compositions comprise an epoxy resin and, optionally,a crosslinker such as a phenolic resin dissolved or dispersed in anorganic liquid. In those compositions containing a crosslinker, thecrosslinker reacts with the epoxy groups on the epoxy resin during thestoving operation so as to form a crosslinked final coating. In knowncompositions the epoxy resin contains bisphenol A diglycidyl ether(abbreviated to BADGE), a commonly available liquid epoxy resin of lowepoxy equivalent weight. Health concerns have arisen over the level ofBADGE appearing in food supplied in cans which have been coated on theinside with epoxy coatings which invariably may contain some unreactedBADGE. Low molecular weight BADGE exists at high levels in low molecularweight commercial epoxy resins while low level of BADGE exists in highmolecular weight epoxy resins. The concern is that all of the BADGE doesnot react with the crosslinker and that some of the residual free BADGEcan leach out of the coating and into the food. As a result of theseconcerns, a limit on the level of free BADGE in the final cured coatingfor the interior of food cans has been proposed based on the amount offree BADGE in the coating and an assumption that all of this couldtheoretically migrate into the food. The current proposal is a limit onthe quantity of free BADGE in the coating such that the contents wouldcontain no more than 1 part per million (ppm) of BADGE if all of theBADGE were to migrate from the coating to the contents. This very lowlevel of free BADGE is not easy to achieve by simple modifications ofthe existing formulations. The problem is particularly acute in smallercans which have a larger interior surface area, and thus more coating,in relation to the volume of contents. The problem is to formulatecoatings suitable for cans which meet the requirements for very low(less than 1 ppm) or zero (non-detectable) levels of BADGE or similarlow molecular weight epoxy-based materials, appearing in food, whileretaining or improving on all the other required characteristics offlexibility, adhesion and sterilisation resistance.

European Patent Application EP-A-0 111 986 discloses pigmented coatingcompositions based on an epoxy-polyester block copolymer in which thepolyester component is prepared by polycondensation of terephthalic acidand/or isophthalic acid and a difunctional hydroxy compound having 2-24carbon atoms. European Patent Application EP-A-0 399 108 disclosessimilar compositions in which the polyester is the condensation productof a carboxylic diacid and a dihydroxy compound in which the componentsare non-aromatic. However neither of these types of polymer are suitablefor use in can coatings because neither gives the required cured filmcombination of flexibility, adhesion and sterilisation resistance andcompatibility. In accordance with this invention, the cured filmproblems have been resolved along with extremely low levels of freeBADGE by the use of a particular epoxy-polyester block copolymer incombination with fatty acids.

According to the present invention, provided is a coating compositioncomprising an organic liquid carrier in which is dispersed or dissolveda mixture of organic film forming components comprising by weight:

i) from 50% to 100% of an epoxy-polyester block copolymer consisting ofthe reaction product of an epoxide terminated epoxy resin and apreformed carboxyl functional polyester polymer,

ii) from 0% to 10% of organic monocarboxylic acid, preferably fattyacid, and

iii) from 0% to 50% of a crosslinker,

where the sum of (i) and (ii) is 100%, characterised in that thepreformed polyester polymer is the reaction product of one or morepolyols, predominantly diol, with dicarboxylic acid or their anhydrides,where the dicarboxylic acids comprise by weight (a) 20% to 45% of anaromatic polycarboxylic acid or its anhydride, (b) 55% to 80%cyclohexane dicarboxylic acid, and (c) 0% to 10% other difunctionalcarboxylic acid, where the sum of (a), (b) and (c) equals 100%, andwhere the epoxy-polyester is optionally further reacted with organicmonocarboxylic acid.

It has been found that this use of a combination of an aromaticpolyfunctional carboxylic acid or its anhydride and cyclohexanedicarboxylic acid in making the polyester gives rise to unexpectedlyimproved properties in the final film, particularly better adhesion,sterilisation and flexibility when compared to the use of eitheraromatic or aliphatic acids alone to produce BADGE-free or low-BADGE(containing less than 1 ppm) can coating compositions.

The resulting epoxy-polyester copolymer is the reaction product of anepoxy resin with a carboxyl functional polyester consisting of residueof the carboxyl functional polyester esterified with the residue of theepoxy resin, where the copolymer contains between 1 and 20 andpreferably between 1 and 10 ester polymeric units. In preferred aspectsof the invention, organic aliphatic monocarboxylic acid, preferablyfatty acid, is further reacted with the epoxy-polyester polymer. Theorganic liquid carrier can be one or more organic liquids in which theepoxy-polyester block copolymer can be dissolved or dispersed. Typicalorganic liquids are aromatic solvents commercially available as Solvesso100□ or Solvesso 150™ from Exxon.

Referring now to the epoxy prepolymer, suitable epoxy resins arearomatic or aliphatic epoxy resins with aromatic epoxy resins beingpreferred. Useful epoxy resins are predominantly linear chain moleculescomprising the coreaction product of polynuclear to dihydroxy phenols orbisphenols with halohyrdrins to produce epoxy resins containingpreferably two epoxy groups per molecule. The most common bisphenols arebisphenol A, Bisphenol F. bisphenol S and 4,4′-dihydroxybisphenol, withthe most preferred being Bisphenol A. Halohydrins includeepichlorohydrin, dichlorohydrih and 1,2-dichloro 3-hydroxypropane, withthe most preferred being epichlorohydrin. Preferred epoxy resinscomprise the coreaction product of an excess of halohydrin withbisphenol to produce predominantly an epoxy group (epoxide) terminatedlinear molecular chain of repeating units of diglycidyl ether ofbisphenol-A containing between 2 and 25 repeating copolymerised units ofdiglycidyl ether of bisphenol-A. In practice, excess molar equivalentsof epichlorohydrin are reacted with bisphenol-A to produce epoxy resinswhere up to two moles of epichlorohydrin coreact with one mole ofbisphenol-A, although less than complete reaction can producedifunctional epoxy resin along with monoepoxide chains terminated at theother end with a bisphenol-A unit. The preferred linear epoxy resins arepolyglydicyl ethers of bisphenol-A having terminating 1,2-epoxide groupsand an epoxy equivalent weight between 150 and 5,000, preferably between150 and 2,000, and a number average molecular weight from about 200 to10,000, preferable from 200 to 5,000, as measured by gel permeationchromatography (GPC). Commercial diglycidyl ether of bisphenol-A (liquidepoxy) can be reacted with additional bisphenol-A to advance the epoxyand increase the molecular weight. The desired molecular weight andfinal oxirane content is controlled by adjusting the ratio of the twocomponents and the extent of the reaction. Commercially available epoxyresins include Dow Chemical epoxy resins identified by trade number andequivalent weights as follows: DER 661(525); DER 664(900); DER 667(3600); and DER 668(5500); while Shell Chemical epoxy resins are EPON1001(525); EPON 1007(2000); EPON 1009F (3000); EPON 1007F (4000); andEPON 1009(6500); and Ciba-Ciegy linear epoxy reins GT-7013(1400);GT-7014(1500); GT-7074(2000); and GT-259(1200). Although not as common,trifunctional epoxy resins are useful comprising branched chain epoxyresins where the branched chains as well as the backbone chain are eachterminated with a terminal epoxide groups to provide greater than twoepoxide functionality. Trifunctional epoxy resins can be produced bycoreacting epichlorohydrin with polynuclear polyhydroxy phenols,trifunctional phenols, or aliphatic trifunctional alcohols.

Useful epoxy resins further include non-aqueous alkylene oxide resinswhich are epoxide functional resins comprising an alkylene oxide adductof a bisphenol compound. The alkylene oxide is an aliphatic alkylderivative having up to about 26 carbon atoms although preferred oxidesare lower alkyl oxides such as ethylene, propylene, and butylene oxides.Bisphenol compounds include bisphenol-A, bisphenol-F and bissulfone orsulfides. Typically two or more moles of alkyl oxide are coreacted withone mole of bisphenol compound. Preferred compositions are 2:1 molarreactions while suitable number average molecular weight range ofalkylene oxide resins is between 200 and 1,000 as measured by GPC. Themost preferred preformed epoxy resin contains two epoxy groups permolecule and the preferred epoxy is based on bisphenol-A.

Referring next to the preformed carboxyl functional polyester, thepolyester comprises polyol, predominantly or entirely a glycol or adiol, esterified with excess equivalents of dicarboxylic acid oranhydrides including considerable amounts of cyclohexane dicarboxyticacid. On a weight basis, the polyester comprises between 55% and 80%cyclohexane dicarboxylic acid, between 20% and 45% aromatic dicarboxylicacid or anhydride, and between 0 and 10% other aliphatic dicarboxylicacid. Useful polyfunctional alcohols have two or more hydroxy groupswhere the predominant polyol contains two hydroxyl groups. Examples ofsuitable polyols include ethylene glycol, 1,4-butane diol, 1,2-propyleneglycol, 1.3-propylene glycol, methyl propane diol, neopentyl glycol,1,6-hexane diol, butyl ethyl propane diol, hydroxy pivolyl hydroxypivalate, cyclohexane dimethanol, trimethylol propane, pentaerythritoland glycerol. 1,4-butane diol is preferred. Minor amounts of glycerol,pentaerythritol, dipentaerythritol or trimethylolethane or propane canbe used if desired. Examples of suitable aromatic dicarboxylic acids arephthalic acid, terephthalic acid or isophthalic acid with isophthalicacid particularly preferred. The anhydride derivatives of these acids analso be used if they exist as anhydrides. The dicarboxylic acid contentof the polyester prepolymer further comprises between 55% and 80%cyclohexane dicarboxylic acid. Preferably less than 10% by weight of thedicarboxylic acid content comprises other aliphatic dicarboxylic acids.examples of other aliphatic polyfunctional carboxylic acids are malonicacid, succinic acid, glutaric acid, adipic acid, azelaic acid, subericacid, sebacic acid, dimer fatty acids, maleic acid and dimer fattyacids. Hydroxy acids can also be included in the polyester such as 12hydroxy stearic acid. lactic acid and 2-hydroxy butanoic acid. Toprovide a carboxyl terminated polyester, the equivalent excess ordicarboxylic acid over polyol is between 0.02 and 0.784, and preferablybetween 0.04 and 0.554. The acid number of the preformed polyestershould be greater than 5 and preferably between 10 and 140 mgKOH/g.

The preformed polyester can be made by heating the components togetherat a temperature of 150 to 280° C., preferably 200 to 250° C. andremoving the water evolved for example by azeotropic distillation withthe aid of an organic solvent such as toluene or xylene. Heating iscontinued until the polyester has an acid number preferably between 10and 140 mKOH/g, more preferably 20 and 110. A catalyst can be used tospeed up the esterification reaction. suitable catalysts are acidcatalysts such as sulphuric acid, paratoluene sulphonic acid or tincatalysts, such as dibutyl tin dilaurate. The hydroxyl number of thepolyester is preferably no higher than 2, and more preferably 0 to 0.8.The number average molecular weight of the preformed polyester ispreferably 800 to 15 000, and more preferably 800 to 8000.

In accordance-with this invention, the epoxy-polyester block copolymercan be prepared by heating the acid functional polyester polymer and theepoxy resin together at a temperature of 110 to 180° C, preferably 120to 170° C. for 1 to 5 hours, preferably 2 to 4 hours. A catalyst for thecarboxyl/epoxy reaction can be included such as triphenyl phosphine,benzyl triphenyl phosphonium chloride, benzyl trimethyl ammoniummethoxide, a tertiary amine such as benzyl dimethylamine or a metalcompound such as zirconium octoate. The reaction can be carried out in asuitable solvent such as toluene or xylene. The weight ratio of thepolyester and the epoxy resin is preferably chosen so that theequivalent ratio of epoxy groups from the epoxy resin to acid groupsfrom the polyester is 1:2 to 2:1, more preferably 1.6:1 to 1:1.6. Theresulting epoxy-polyester block copolymer preferably has a numberaverage molecular weight of 3 000 to 40 000, and a low Acid Number below10 and preferably less than 1 mgKOH/g.

In a preferred aspect of this invention, the epoxy-polyester blockcopolymer is further reacted with an organic monocarboxylic acid,preferably an aliphatic monocarboxylic acid, and most preferably analiphatic fatty acid having a fatty acid chain of 8 to 24 carbon atoms.The most preferred fatty acids ordinarily are derived from vegetableoils or fats which conventionally contain a mixture of glyceride oilscomprising glycerol esters of fatty acid. Fatty acids are typicallyobtained by hydrolysis of vegetable oils or fats. Useful fatty acidsinclude lauric acid, capric acid, palmitic acid, stearic acid, oleicacid, linoleic acid, linolenicacid, eleostrearic acid and ricinoliecacid. The preferred fatty acid is coconut fatty acid. Less preferredlower aliphatic monocarboxylic acids can include formic acid, aceticacid, propionic acid, n-butyric acid, isobutyric acid, n-valeric andisovaleric acids, pivalic acid, and capronic acid. less preferredaromatic monocarboxylic acid include benzoic and toluic acids. Inaccordance with this invention, the organic monocarboxylic acid is postreacted with unreacted epoxide associated with the prior formedepoxy-polyester block copolymer.

Surprisingly it has been found that the levels of free epoxy resin(particularly low molecular weight resin such as BADGE) in the finalcomposition can be further reduced by heating the block copolymer in thepresence of an acid or a base, of which phosphoric acid has been foundparticularly effective. The copolymer can be heated in the presence ofthe phosphoric acid or base for example for 30 to 240 minutes at 100 to200° C., preferably 1-3 hours at 120 to 180° C. Preferred bases aredimethyl benzylamine, diethylene triamine, and tributyl amine. The acidor base can be added at levels of, for example, 0.2 to 10% by weightbased on the polymer solids, preferably 0.5 to 10%. Such treatment canreduce the level of free epoxy resin below normally detectable limits.

Preferably the composition comprises at least 1% by weight ofcrosslinker and more preferably comprises from 50 to 97 parts by weightof epoxy-polyester block copolymer and 3 to 50 parts by weight ofcrosslinker. The crosslinker is a material which will react with theepoxy polyester to give rise to a crosslinked final coating. Examples ofsuitable crosslinkers are phenolic resins, amino resins and blockedpolyisocyanates. Preferably the crosslinker is a phenolic resin.Phenolic resins are reaction products of phenol compounds withformaldehyde, and are divided into resols in which the reaction is basecatalysed and novolacs in which the reaction is acid catalysed. When across linker is used, the coating compositions can also contain acatalyst for the reaction between the remaining epoxy groups on theepoxy polyester polymer and the phenolic resin such as phosphoric acid.The compositions can be made by mixing the components in any order, suchas by adding the epoxy-polyester block copolymer and the crosslinker tothe organic liquid carrier.

The compositions also preferably contain finely divided PVC, in whichcase the liquid medium is chosen so as to dissolve the PVC polymer toonly a minor extent or not at all. Such compositions are referred to asPVC organosols. PVC organosols are particularly known for theirflexibility and sterilisation resistance properties and are used forcans containing some of the more aggressive products, such asacid-containing foods. They are also used for “easy open ends”, that isto coat the inside of food or drink cans is which the metal (usually thelid, or part of the lid) is partially cut through during manufacture tofacilitate opening of the can by the consumer using a ring-pull orsimilar opener. Where PVC is used, the epoxy resin is found to stabilisethe PVC polymer against decomposition during curing of the compositionafter it is applied to the metal. Useful PVC is preferably finelydivided polyvinyl chloride in powder form is commercially available froma number of sources. Preferably the PVC powder has a particle size rangeof 0.5 to 12 μm. Examples of suitable commercially available PVC powdersare Geon 171™ (from the Geon Company) and Vinnol P70™ from WackerChemie). Preferred compositions comprise 10 to 80 weight % of PVC basedon the total non-volatile weight of epoxy-polyester block copolymer,crosslinker and PVC, more preferably 20 to 70 weight %. The PVC ispreferably added to the compositions by what is known as a grindingprocess using a ball mill or sand mill.

Preferably the compositions are pigment free when they are for use incoating the interior of cans. Pigments tend to be a source of weaknessin such coatings and are often detrimental to their performance. Othercomponents of the compositions can be waxes and flow additives as wellas other conventional coating components. The compositions preferablycontain less than 1 ppm of BADGE, more preferably less than 0.5 ppm andmost preferably below detectable limits.

The compositions can be applied as coatings to a variety of substratessuch as plastic, glass or metal but are particularly suited to coatingmetal. In particular they are useful in coating food or beverage cans,especially the interiors of such cans where their low or undetectableBADGE content and their other properties make them particularlydesirable. The composition can be applied as a film by conventionalmeans such as brushing, roller coating or spraying. Roller coating isthe preferred method when coating flat metal for can manufacture andspraying is preferred when coating preformed cans.

The applied film of the composition can be dried and cured by heating todrive off the organic liquid and to accelerate the crosslinking reactionbetween the epoxy-polyester and the crosslinker. The composition istypically heated to 150-220° C. for 1 to 20 minutes in order to from adried, cured film. A so-called “flash-stoving, i.e 10-30 seconds at apeak metal temperature of 220-260° C. can also be used.

Another type of stoving is induction curing i.e. 4-6 seconds at a peakmetal temperature 280-320° C. PMT. Compositions were evaluated ontinplate for use on easy-open ends. Easy open ends require curedcoatings exhibiting high flexibility and sterilisation resistance, aswell as the normal tests, wedge bend drawn cans and ends. Goodresistance to feathering which is the uneven tearing of the film at theeasy open end edge on opening is also required. A test for feathering isas follows:

A 5 cm×10 cm panel coated with the composition is placed on a flexiblesupport—rubber pad, wads of paper. The internal coating to be evaluatedis in contact with the support. On the back of the panel, a metal ruleris placed and the metal is scored with a scalpel longitudinally,perpendicular to the metal grain at a distance of about 1-1{fraction(1/2 )} cm from the edge. There is now a longitudinal bump on theinternal coating. The metal is then cut with scissors about 1 cm alongthe groove/bump and the approximately 1{fraction (1/2 )} cm width isgripped in a sardine can opener and the strip is rolled slowly aroundthe opener—exactly as when opening a can. The metal panel is then turnedover and the edge of the flat part examined with the naked eye and witha magnifying glass. Ideally the interior coating should not go beyondthe metal. A slight amount of varnish detached from the rolled part istolerated—width 0.5 mm. This varnish should be a uniform strip, and notpresent a feathered appearance—which is indicative of detached varnishparticles which could fall into the food/beverage. This method is asevere control, since if done quickly i.e.. at the speed of opening acan, then the cut edge should be perfect. This test is carried out onnon-sterilised and sterilised panels.

The invention will now be illustrated by means of the followingexamples;

EXAMPLES

A series of 14 compositions were made, applied to metal panels, stovedand then subjected to adhesion, and sterilisation resistance tests. Thecompositions generally comprised an epoxy-polyester block copolymer anda PVC powder carried in an organic liquid. The compositions were made byfirst making a polyester polymer, reacting this with an epoxy resin soas to form an epoxy-polyester block copolymer and then dispersing a PVCpowder into a solution of the block copolymer.

1. Preparation of Polyester Polymer

The following general method was used to produce a series of 15polyester polymers using the components listed in Table 1.

The components from Table 1 were heated to 235° C. with stirring undernitrogen in apparatus equipped with a fractionating column and condenserfor removing water. The components were heated with removal of wateruntil the reaction product in the flask had an acid value of 49-51mgKOH/g of non-volatile material. About 3 parts of xylene were addednear the end of the process when removal of water becomes slow. Theabbreviations for Table 1 are given after the table. In Table 1 the mainfigures relate to parts by weight and those in brackets refer to molarparts.

In order to anticipate glycol losses during processing, the quantitiesof 1,4 butanediol or other glycol are increased by 3% over that requiredto give the desired functionality. In the event the Acid Value remainsabove the desired 49-51 mgKOH/g, then a minimal amount of suitableglycol is added to sufficiently lower the Acid Value and compensate forglycol losses greater than the anticipated 3%.

TABLE 1 EXAMPLE NUMBER Component 1 2 3 4 5 6 7 8 Polyfunctional Alcohols1,4-butane diol 266.35 259.23 262.83 261.92 264.66 284.77 239.59 248.81(2.959) (2.880) (2.920) (2.910) (2.941) (3.146) (2.662) (2.765)neopentyl glycol 102.87 100.12 101.52 101.17 102.23 109.03 93.37 96.97(1.099) (0.963) (0.976) (0.973) (0.983) (1.048) (0.898) (0.932)Polyfunctional acids Isophthalic acid 726.97 358.55 267.99 541.58 288.80247.34 256.86 (4.379) (2.160) (1.614) (3.263) (1.740) (1.490) (1.547)1,4-cyclohexane 733.10 371.51 462.80 187.05 dicarboxylic acid (4.262)(2.160) (2.691) (1.088) adipic acid 423.34 (2.90) sebacic acid 501.63(2.483) azeleic acid 484.83 (2.579) Fascat 4102 1.30 1.30 1.30 1.30 1.301.30 1.30 1.30 CHARACTERISTICS Polyester Acid 1.97 1.97 1.99 1.99 1.991.99 1.94 1.98 Functionality Theoretical MW 2314 2246.0 2274.0 2263.02290.0 2289.0 2216.0 2302.0 by number Weight of solid 583.20 DER 671(EEW 485) Acid value of 1.10 0.14 0.22 0.30 0.32 0.00 0.21 0.10 epoxypolyester mg/g EEW of epoxy 5090.0 4990.0 4670.0 4680.0 4360.0 4480.04370.0 4430.0 polyester Theoretical MW 8841.0 8319.0 8547.0 8612.08940.0 8971.0 8273.0 9043.0 by number Solid content 47.5% 48.4% 50.2%47.2% 51% 49.8% 49.7% 49.8% 200° C. 10 mins Viscosity poises 61.00 17.0029.00 61.00 46.00 23.00 43.00 31.00 EXAMPLE NUMBER Component 9 10 11 1213 14 15 Polyfunctional Alcohols butane diol 354.64 239.13 (3.940)(2.657) neopentyl glycol 101.17 93.37 87.36 84.05 76.39 93.28 (0.973)(0.898) (0.84) (0.808) (0.735) (0.897) methyl propane diol 261.92(2.910) 1,6-hexane diol 314.12 (2.662) 1,6-cyclohexane 354.37 dimethanol(2.461) butyl ethyl propane diol 376.52 (2.353) hydroxypivalyl 427.74hydroxypivalate (1.998) Polyfunctional acids isophthalic acid 271.94267.99 247.33 231.40 222.63 202.36 168.16 (1.638) (1.614 (1.490) (1.394)(1.341) (1.219) (1.013) 1,4-cyclohexane 469.62 462.80 427.11 399.61384.47 349.46 581.15 dicarboxylic acid (2.730) (2.691) (2.483) (2.323)(2.235) (2.032) (3.379) Fascat 1.30 1.30 1.30 1.30 1.30 1.30 1.30CHARACTERISTICS Acid Functionality 1.99 1.98 1.94 1.96 1.95 1.97 1.972of polyester Theoretical 2297.00 2262.00 2216.00 2232.00 2225.00 2248.001143.00 MW by number Weight of solid dER 583.20 671 (EEW 485) Acid valueof epoxy 0.10 0.18 0.37 0.13 0.12 0.07 polyester mg/g Polyester Epoxy4400.00 4360.00 4340.00 3525.00 4023.00 4416.00 equivalent weightTheoretical MW by 8919.00 8689.00 8273.00 8408.00 8376.00 8547.00 numberSolid content 200° C. 50.1% 50.4% 50% 48.2% 50.4% 50.7% 10 minsViscosity poises 43.00 22.00 55.00 43.00 13.00 13.00

Fascat=Fascat 4102™, a tin based esterification catalyst from CecaAtochem.

2. Preparation of Epoxy Terminated Epoxy-polyester Block Copolymer

2.1. Epoxy-polyester Block Copolymers 1 to 14

Solvesso 150 (a high boiling aromatic solvent from Exxon, 181 parts) wasadded to the polyester polymers 1 to 14 prepared in 1 above (954 parts)followed by an epoxy resin (DER 671X75™ from DOW, 778 parts at 75%solids in xylene) The resulting mixture was diluted to a theoreticalsolids content of 70% by addition of methoxypropyl acetate (92 parts)and Solvesso 150 (182 parts). Triphenyl phosphine (2.22 parts ) wasadded and the mixture was heated to 145-150° C. until the measured acidvalue was 0.5 mgKOH/g or less and the epoxy equivalent weight is 3500 to4500. The resulting epoxy-polyester block copolymer was diluted to asolids content of 47.5-50% depending on viscosity, with a 29/17/54 blendof Solvesso 150, Solvesso 100 (a high boiling aromatic solvent fromExxon) and methoxy propanol.

2.2 Carboxy Terminated Epoxy-polyester Block Copolymers 16 to 17

Solvesso 150 (a high boiling aromatic solvent from Exxon, 181 parts) wasadded to the polyester polymer 15 prepared in 1 above (954 parts)followed by an epoxy resin (DER 671×75 from DOW, at 75% solids inxylene) in amounts set out below. In Examples 16 to 18 below, the ratioof polyester to epoxy varied as indicated.

Polyester Amount of epoxy resin Ex 15 (954 g. solids) 497.62 g (0.517mols) For Example 16 Ex 15 (954 g. solids) 665.58 g (0.685 mols) ForExample 17 Ex 15 (954 g. solids) 746.98 g (0.769 mols) For Example 18

3. Preparation of Coating Compositions 1 to 14

Coating compositions 1 to 14 were made from the components listed inTable 2 below. Components 1 to 5 were ground together and components 6to 12 were subsequently added in the order given. The resulting coatingcompositions had a solids content of around 46-48% and had a viscositysuitable for roller coating. The coatings have the same number as theepoxy-polyesters in Table 1.

Number Component Parts by wt. 1.00 Solvesso 100 135.46 2.00 methoxydipropanol 135.46 3.00 Epoxy-polyester block copolymer from Table 1295.42 4.00 Wax 8.76 5.00 PVC 289.38 6.00 Phosphoric acid (75% aqueoussolution) 1.27 7.00 methoxy dipropanol 5.06 8.00 HEH 0960 Phenolic resin(Holden) 65.22 9.00 RS 136 Phenolic resin (Holden) 11.28 10.00 FVH 1634Catalyst (Holden) 9.49 11.00 Solvesso 100 21.61 12.00 methoxy dipropanol21.61

Unfortunately it proved impossible to incorporate polymer 1 into acoating composition with PVC as the mixture solidified duringpreparation.

Preparation of Comparative Coating Composition 19

Epoxy-polyester block copolymer 4 at 48.0% solids by weight was heatedat 136° C. to 138° C. (Reflux) with 0.2% phosphoric acid for one hour,then cooled and diluted in 1:1 solvessol 100 and methoxy dipropanol to45% solids. This modified copolymer was used to make coating composition19 in exactly the same method as that used above for compositions 1 to14 with the weight for weight replacement of the phenolic resins HE 0960and RS 136 with Phenodur 285™ (from Hoechst) and the use of a higherlevel 3.38 parts of wt. of phosphoric acid (75% Aq. solution). Theresulting coating was substantially free of BADGE and gave reasonablesterilisation results on tin plate. Results on T.F.S. (tin free steel)were not as good.

4. Testing

Compositions 2 to 14 were applied onto panels of tin free steel and tinplate at a film weight of 12 g/m2 and stoved for 15 minutes at a peakmetal temperature of 190° C. Specimens with dimensions of about 12.5×5cm were cut out from these panels and the cured films were subjected tothe following tests;

Wedge Bend

The test panel was bent longitudinally through 180° over a 6mm mandreland then removed from the mandrel and a standard weight wedge shaped wasdropped from a standard height onto the panel to create a sharp conicalbend. The bend is then placed in acidified copper sulphate which revealsany metal uncovered by copper deposition. The panel is dried and thenScotch™ tape (grade 3M™ 610 ) was firmly stuck all along the bend andripped off to reveal any loss of adhesion. The results are ratedaccording to the percentage coating remaining along the length of thebend.

Sterilisation Resistance

Bent panels were prepared as for the wedge-bend test and then sterilisedat 130° C. for 1.5 hours in a solution of 1% sodium chloride and 2%tartaric acid. The coating on the bends are then visually examined. Awhitening of the film indicate poor sterilisation resistance as doesblistering. These sterilised wedge bends are then scotch taped as aboveto determine adhesion after sterilisation.

5. Test Results

Wedge Bend Composition Flexibility Adhesion Sterilisation Resistance 1 —— — 2 100% No Loss Poor 3 100% Great Loss Good 4 100% No Loss Good 5 88%Slight Loss Poor 6 88% Great Loss Very Poor 7 82% Great Loss Very Poor 882% Great Loss Very Poor 9 100% Slight Loss Very Poor 10 100% No LossGood 11 100% No Loss Good 12 100% No Loss Good 13 82% No Loss Very Good14.00 82% No Loss Very Good

TABLE 4 INGREDIENT EXAMPLE WEIGHT (Moles) 16* 17 18 1.4 Butanediol239.13 (2.657) Ditto Ditto Neopentyl Glycol  93.28 (0.897) Ditto DittoIsophthalic Acid 168.16 (1.013) Ditto Ditto 1.4 Cyclohexane DicarboxylicAcid 1581.15 (3.379)  Ditto Ditto Acid Value of Polyester mg/g 110 mg/gAcid Functionaty 1.97 Molecular weight by number 1143 Weight (moles¹)Solid E1001. 497.62 (0.517) 665.58 (0.685) 746.98 (0.769) MW+=972.EEW=486 CHARACTERISTICS OF THE EPOXY-POLYESTER Solids 50.4% 47.7% 47.7%Viscosity 15 poises 54 poises 118 poises Acid value 25.4 mg/g 11.2 mg/g6.8 mg/g Epoxy Equivalent Weight 54340 25230 20000 *A version of thisexample was made in EEP and had an undetectable BADGE level. The normalie. Solvesso 100 containing version was evaluated as an organosol as inExamples 1-14 and found to have poor sterilisation resistance butexcellent flexibility and adhesion. The other examples have not yet beenevaluated. In view of their very high EEW, they could avoid H3PO4treatment. Even if not sterilisable, they could be used in pasteurisableformulae.

Example 16—to the above are added 178.5 parts sol.150, then the epoxy,then 92 parts methoxy propyl acetate, then 178.5 sol. 150 Triphenylphosphine 2.03 parts. Heated to a constant acid value of around 26 mg/g.

Example 17—to the above are added 186 parts sol. 150, then the epoxythen 92 parts methoxy propyl acetate, then 186 parts solvesso 150.Triphenyl phosphine 2.27 parts. Heated to a constant acid value ofaround 12 mgKOH/g.

Example 18—to the above are added 190 parts solvesso 150, then theepoxy, then 92 parts methoxy propyl acetate then 190 parts solvesso 150.Triphenyl phosphine 2.38 parts. Heated to a constant acid value ofaround 7 mgKOH/g.

7. Example 20. Preparation of a Fatty Acid modified epoxy-polyester LX190/101/2

7.1. The ingredients and weights of Example 4 reproduced as follows wereprocessed according to the method described in Section 2.1 above.

butanediol 261.92 (2.910) neopentyl glycol 101.17 (0.973) isophthalicacid 267.99 (1.614) 1,4-cyclohexane dicarboxylic acid 462.80 (2.691)FASCAT 1.3

Then add 583.2 g solid DER 671 and other components indicated in Section2.1 above, except at Acid Value less than 0.5 mg./g and while still at145 to 150° C. and 70% NVM solids by weight, the following ingredientswere added:

Coconut fatty acids (Prifac 7907 TM, Umchemcia Int.) 61.5 g which is 4%by wt. based wt. of epoxy-ester Methoxy propyl acetate 25.39 g ResiflowFL2 (Worlec) antifoam agent Dimethyl ethanolamine (0.2% on resin solids)

The resulting resin, still at 70% NVM resin solids, is then heated toreflux (155° C. to 165° C.) and maintained for 1.5 to 2.5 hours untilthe resin Acid Number is below 1 and the epoxy equivalent weight is 9000to 11000. The resin was further diluted in accordance with 2.1. Theresulting modification provided a resin essentially free of BADGE.

8. Example 21; using fatty acid modified epoxy-polyester of Example 20

Solids 1) Epoxy-polyester Ex. 20 302.88 143.57 2) PVC 292.99 292.22 3)WAX VM47 7.24 / 4) Solvesso 100 129.65 / 5) Methoxy propanol 129.64 / 6)FVH 1634 17.94 / 7) Phosphoric acid 20% solution in Butanol 7.88 / 8)Rutaphen LB7700 (Bakelite) 111.78  78.25 1000.00 514.81

Percentage solid composition: PVC 56.9%; modified epoxy-polyester 27.9%;phenolic resin 15.2%. Viscosity=94 seconds AFNOR 4 Cup at 25° C.

Ingredients 1-5 were pre-mixed with a COWLES Blade, then ground forabout 20 minutes in a sand grinder. The temperature was allowed to go to37-38° C. Ingredients 6-8 were added and the resultant product appliedat 20 g/m2 onto tinplate and stoved 4-6 seconds with a laboratoryinduction equipment.

Test results for head cured coating film of composition Example 21 areshown in Table 5 below.

TABLE 5 STERILISATION 130° C. 1½ HOURS BEFORE (Feathering-Varnish widthafter sterilisation) WEDGE STERILISATION ASYMMETRIC 1% Citric + PanelBEND (VARNISH WIDTH) CAN 3% Acetic Acid 2% Tartaric Acid 1% Salt 1% Salt½ water/steam 100% 0.5 mm All 4 angles and OK OK Slight Whitening OKSlight whitening shoulder good (0.2 mm) (0.2-0.3 mm) of film (0.2 mm) orde-coloration

9. Example 22

Conventionally stoved organosol using fatty acid modifiedepoxy-polyester.

MIXTURE 119 SOLIDS % 1) Epoxy-polyester Ex. 20 (47.6% 278.29 132.4729.93 solids) 2) VM 47 wax 8.12 259.61 3) PVC 259.61 58.66 4) Solvesso100 121.06 5) Methoxy Dipropanol 121.06 6) Phosphoric acid 20% inButanol 8.51 7) HEH 0960 (49% solids) or Phenodur 59.58 29.19 6.60 2858) RS 136 (50% solids or alternative 10.25 5.13 1.16 phenolic 9) FVH1634 (30% solids) 12.93 / 10) Cymel 1123 (98%) DYNO 4.40 4.31 0.97CYANAMID 11) Dynapol LH 826 (55% solids) 21.60 11.88 (HULS) 12) Solvesso100 47.29 2.68 13) Methoxy Dipropanol 47.29 1000 442.59 100

As before, components 1 to 5 were pre-mixed with a cowles blade, thenground in a sand mill for about 20 minutes, preventing the temperaturefrom rising above 37-38° C. The other ingredients were added with simplestirring. The organosol was applied at 18 mg/m² into tinplate and T.F.S.and stoved for 15 minutes with 9 minutes at a peak metal temperature of190° C.

The test results on cured coating films from composition Example 22 areshown in Table 6 below.

TABLE 6 Flexibility 94% WEDGE BEND Adhesion OK Sterilisation ResistanceGood on Tinplate and TFS (a) 1% salt solution (130° C. for in:- (b) 1%citric acid 1 hr. 30 min) (c) 1% salt

What is claimed is:
 1. A protective coating composition in an organicliquid carrier comprising a polymeric film forming binder, the polymericbinder comprising by weight: (a) 50 to 100% of an epoxy-polyester blockcopolymer being the reaction product of a preformed epoxy resin and apreformed carboxyl functional polyester prepolymer, and (b) 0 to 50% ofa crosslinker where the sum of (a) and (b) is 100%, characterized inthat the carboxyl functional polyester prepolymer is the reactionproduct of one or more polyols with one or more dicarboxylic acids ortheir anhydrides, where the dicarboxylic acids or anhydrides comprise amixture of (i) 20% to 45% of an aromatic dicarboxylic acid or itsanhydrides, (ii) 55 to 80% of cyclohexane dicarboxylic acid, and (iii) 0to 10% other aliphatic dicarboxylic acid, where the sum of (i), (ii),and (iii) is 100% based on the weight of the dicarboxylic acid andanhydride components, which also comprises finely divided polyvinylchloride (PVC) of a particle size of 0.5 to 12 microns, where theorganic liquid carrier does not dissolve the PVC.
 2. A composition asclaimed in claim 1 which comprises 20% to 70% of PVC based on the totalweight of epoxy-polyester block copolymer plus crosslinker plus PVC. 3.A process of coating metal cans which comprises the steps of: applying alayer of a protective coating composition in an organic liquid carriercomprising a polymeric film forming binder, the polymeric bindercomprising by weight: (a) 50 to 100% of an epoxy-polyester blockcopolymer being the reaction product of a preformed epoxy resin and apreformed carboxyl functional polyester prepolymer, and (b) 0 to 50% ofa crosslinker where the sum of (a) and (b) is 100%, characterized inthat the carboxyl functional polyester prepolymer is the reactionproduct of one or more polyols with one or more dicarboxylic acids ortheir anhydrides, where the dicarboxylic acids or anhydrides comprise amixture of (i) 20% to 45% of an aromatic dicarboxylic acid or itsanhydrides, (ii) 55 to 80% of cyclohexane dicarboxylic acid, and (iii) 0to 10% other aliphatic dicarboxylic acid, where the sum of (i), (ii),and (iii) is 100% based on the weight of the dicarboxylic acid andanhydride components, and drying and curing the coating by heating.